[1] "YATSUra" is the plural form of "yatsu," which is a slang term for "you." It can be downright rude and offensive to use. Something like "Those scum, bastards, low-lives, scoundrels," etc.
[2] "RASSE" and "RASSERA" don't really mean anything. This chant is shouted during the Nebuta festival held from August 2-7 in Aomori. It's supposed to shake away the sleepiness of summer. For more information, try out these sites (brought to my attention by Chris Condrat ^_^):